Formation of decagonal and approximant phases in the Al-Ni-Ru system

Al-Ni-Ru alloys with a wide composition range have been synthesized and examined by X-ray and electron diffraction experiments. In this system, two types of decagonal (d) phases are formed, namely basic-type and superlattice-type d phases. Annealing experiments have shown that the basic-type d phase is stable at high temperatures and that its single-phase region is located in a small composition range around Al 75 Ni 15 Ru 10 . On the other hand, the superlattice-type d phase is metastable and has been found to form only in the samples before annealing. Besides the d phases, a high-order crystal approximant phase with lattice parameters a = 99.5 Å and b = 84.6 Å has been found. The structural relation between the approximant phase and the d phase is discussed in terms of a phason tensor.     

Pressure-Induced transitions in amorphous TlxSe100−x alloys

Abstract

The electrical resistivity of bulk semiconducting amorphous Tl_xSe_100?x alloys with 0 ≤ x ≤ 25 has been investigated up to a pressure of 14 GPa and down to liquidnitrogen temperature by use of a Bridgman anvil device. All the glasses undergo a discontinuous pressure-induced semiconducting-to-metal transition. X-ray diffraction studies on the pressure-recovered samples show that the high-pressure phase is the crystalline phase. The pressure-induced crystalline products are identified to be a mixture of Se having a hexagonal structure with a = 4·37 Å and c = 4·95 Å and TlSe having a tetragonal structure with a = 8·0 Å and c = 7·0 Å     

Twin formation and structural modulations in orthorhombic and tetragonal YBa2(Cu1-xCox)3O7-δ

Abstract

The microstructure of YBa₂(Cu_1?xCo_x)₃O_7?δ, prepared by the standard ceramic method, shows lamellar twin structures with decreasing spacings between twin walls with increasing Co content for x?0·02, developing into {110}-type cross-hatched ‘tweed’ modulation for x?0·02. Several wall junctions are found for x=0·02. The structural phase transition between macroscopically orthorhombic and tetragonal material occurs at x≈0·025; structural modulations (λ≈20Å) persist in the samples with high Co content (x>0·25). The modulations lead to a considerable broadening of the X-ray lines affected by orthorhombic splitting, and show maximum amplitude at the critical composition x≈0·025.     

Energy-based structure prediction for d(Al70Co20Ni10)

We use energy minimization principles to predict the structure of a decagonal quasicrystal–d(AlCoNi)–in the cobalt-rich phase. Monte Carlo methods are then used to explore configurations while relaxation and molecular dynamics are used to obtain a more realistic structure once a low-energy configuration has been found. We find five-fold symmetric decagons 12.8?Å in diameter as the characteristic formation of this composition, along with smaller pseudo-five-fold symmetric clusters filling the spaces between the decagons. We use our method to make comparisons with a recent experimental approximant structure model from Sugiyama et al. (K. Sugiyama, S. Nishimura and K. Hiraga, J. Alloy Comp. 342 65 (2002)).     

Approximant phases,phason planes and domain-boundary networks in Al−Ni−Rh alloys

Structurally complicated ξ′- and ξ-phases have been found, for the first time, in as-cast Al₇₃Ni₅Rh₂₂ and Al₇₅Ni₁₅Rh₁₀ alloys. The lattice parameters of these two phases were determined by means of electron diffraction and high-resolution transmission electron microscopy (HREM). These two phases have similar orthorhombic structures but with different lattice parameters of a?=?23.2?Å, b?=?16.4?Å, c?=?12.0?Å for the ξ′-phase and a?=?20.3?Å, b?=?16.4?Å, c?=?14.8?Å for the ξ-phase. A new two-dimensional domain-boundary network has also been observed in these two phases. Domain boundaries with normals closely parallel to the [001] direction are actually phason planes represented by a translation vector of r?=(1/2)a?+(1/2τ)c in the ξ′-phase and r=±(1/2τ²) a?+(τ/2)c in the ξ-phase, whereas the newly-found wide and zigzag boundaries perpendicular to the above set were attributed from the step-like boundary structures of domains related by a translation vector of r?=(1/τ)((1/2)a?+(1/2τ)c). The structural difference between the two types of planar faults is discussed.     

A cubic approximant in the Zn-Mg-Er alloy

A cubic approximant for the icosahedral phase is found in the Zn-Mg-Er system. The preparation of the Zn-Mg-Er ternary phase (the so-called R phase) through quenching and annealing is described in detail. The R phase was found by means of scanning electron microscopy in combination with wavelength-dispersive X-ray analysis. The composition of the R phase varies around Zn₆₃Mg₂₃Er₁₄ in different samples depending on the initial composition. The structure has been studied by a combination of high-resolution transmission electron microscopy (HRTEM) and X-ray powder diffraction. The R phase is cubic with a ₀ = 2.02 nm and crystallizes in the space group F 43m. The close relationship of this phase to the icosahedral phase in the Zn-Mg-Y, RE system (RE = rare earth) is demonstrated through electron diffraction features and HRTEM images.     

Preparation of decagonal Zn-Mg-Y by melt spinning

It is shown, for the first time, how pure decagonal Zn-Mg-Y can be prepared by melt spinning and annealing. Study of the phase formation was performed by differential scanning calorimetry and the sample was further investigated by X-ray and electron diffraction. The lattice constants of the decagonal phase are a q =4.592Å and c =5.198Å calculated from a physical space model, or a q =4.485Å and c =5.193Å from a hyperspace model.     

Crystal structure of 1–2–3 superconductor precursor material: Vacancy distribution and lattice relaxation

Abstract

The crystal structure of tetragonal YBa₂Cu₃O_7-δ, with δ close to the critical composition for the tetragonal–orthorhombic transition, has been refined. The oxygen deficiency δ = 0·65(10) is accommodated by both the O(1) and O(2) sites which coordinate the ‘square planar’ Cu(1) site. Structural relaxation around the vacancies is indicated by large anisotropic Debye-Waller ellipsoids in the structural layer formed by these atomic sites. The Y, Ba, Cu(2) and O(3) sites are not involved in the relaxation mechanism. On comparing this structure with the δ ≈ 0 and δ ≈ 1 end-members, we find that with decreasing oxygen content of the structure the Cu(2) valence type transforms from square-pyramidal character towards square-planar character. This effect gives the main contribution to the increase of the c ₀ lattice constant with decreasing oxygen content.     

Formation and hydrogen adsorption properties of Ti-Hf-Ni quasicrystals and crystal approximants

The formation of a high-order rational approximant (RA) phase in rapidly quenched Ti-Hf-Ni alloys and the hydrogen absorption properties of that phase are reported. Electron diffraction patterns show systematic shifts of the diffraction spots from their expected positions for the icosahedral phase (i-phase); the diffraction patterns are consistent with those expected for a 3/2 RA phase RA-(Ti-Hf-Ni). Based on differential scanning calorimetry studies, RA-(Ti-Hf-Ni) is metastable, transforming between 350 and 500°C to a quasicrystal with strong phason disorder. This crystallizes at 620°C to a Ti 2 Nitype phase. RA-(Ti-Hf-Ni) readily absorbs hydrogen, up to 1.2 hydrogen atoms per metal atom ([H][M] =1.2). Pressure-composition isotherm studies for gasphase loading show that the pressure plateau for RA-(Ti-Hf-Ni) is similar to that observed for the i-(Ti-Zr-Ni) phase, although it occurs at as lightly higher pressure and extends over a smaller range of hydrogen concentrations. Unlike i-(Ti-Zr-Ni), no irreversible hydride phase forms with hydrogen loading at 250°C, suggesting that RA-(Ti-Hf-Ni) may have superior cycling properties, of interest for hydrogen storage applications.     

Transformational leadership,psychological empowerment,and flow at work

ABSTRACT

Frequent experiences of flow – an enjoyable state of optimal challenge – at work are associated with many positive individual and organizational outcomes. In our research, we examine how leaders affect subordinates’ flow experiences through subordinates’ work-related self-concept. Specifically, on the basis of self-concept theory, we propose that transformational leaders affect followers’ work-related self-concept, which we construe as followers’ psychological empowerment, consisting of the four sub-facets of meaning, competence, self-determination and impact. We further propose that psychological empowerment is positively related to flow experiences at work. In sum, we thus hypothesize that the effect of transformational leadership on employees’ flow experiences is mediated by psychological empowerment. Additionally, we propose that this indirect effect is moderated such that it is stronger for employees holding a formal leadership position. We tested the model with two two-wave questionnaire studies with employees (Study 1: N = 307 at time 1; N = 60 at time 2; Study 2: N = 611 at time 1; N = 271 at time 2) from different organizations. Path models reveal support for the mediation hypotheses in both samples but not for the moderated mediation hypothesis.     

The effects of stressors and coping resources on anxiety and peripheral narrowing

Abstract

The purpose of the study was to examine possible mechanisms which might help explain why individuals with high life stress and/or low coping resources are at greater risk for incurring athletic injuries. The effects of life events, daily hassles (DH), and coping resources (CR) on state anxiety and peripheral vision narrowing during a stress condition were examined. Subjects were 74 recreational athletes who completed the Life Events Survey, Daily Hassles Scale (DHS), Vulnerability to Stress Questionnaire (CR), and state portion of the State-Trait Anxiety Inventory. Peripheral vision was measured alone during baseline and while simultaneously performing a Stroop Color-Word Test accompanied by distracting noise during the stress condition. State anxiety was assessed during baseline and the stress condition. Analyses of covariance revealed that high negative life events (NLE) (p = .01) were related to greater peripheral narrowing during the stress condition. High TLE (p = .01) and DH (p = .005) were related to elevated state anxiety during the stress condition. The peripheral vision TLE main effect (p = .03) and the state anxiety interactions of NLE × CR and DHS × CR (ps = .05) approached significance. High CR tended to reduce perceived state anxiety during the stress condition for high NLE and DH subjects compared to similar subjects with low CR. Thus, partial support was offered for the mechanisms proposed in the Andersen and Williams (1988) stress-injury model. The results are discussed in terms of future research needs.     

Religion and Prejudice Toward Immigrants and Refugees: A Meta-Analytic Review

ABSTRACT

Religion is often a driving force in negative attitudes; however, in the specific case of migrant-based attitudes, research has produced conflicting findings. That is, religion can paradoxically facilitate either tolerance or intolerance toward this group. In light of these inconsistent findings, we conducted a meta-analytic review to estimate the effect size of this relationship with two major aims—first, to explore differences as a function of how religion was operationalised, and second, to explore differences in the target migrant-type (e.g., differences in religion-based attitudes toward immigrants and refugees/asylum seekers). Our search strategy was applied to PsycINFO, EBSCO Psychology and Behavioural Sciences Collection, Web of Science, PsycEXTRA, and ProQuest Central for peer-reviewed English language studies and made calls for unpublished data through relevant professional bodies. This search strategy yielded 37 records (including 43 studies; N = 472,688). Religion was quantified in two ways: either as categorical religious affiliations (k = 60) or as individual differences in self-reported religiosity (k = 30). The meta-analyses revealed that religion quantified as affiliation, but not religiosity, was related to negative migrant attitudes. Specifically, religiously affiliated samples report more negative attitudes than nonreligious affiliated samples, and this effect was often stronger when the target groups were refugees rather than immigrants. In addition, analyses revealed that Muslims have more negative attitudes toward migrants than Christians. Religiosity was unrelated to negative attitudes. These findings are discussed in light of rising antimigrant attitudes.     

Orthorhombic approximant phases and their relation to quasicrystals in mechanically alloyed Al–Cu–Fe–Si alloys

The possibility of synthesis of quasicrystalline and associated approximant phases during mechanical alloying and subsequent heat treatment of Al₆₅Cu₂₀Fe₁₀Si₅ alloy powders has been investigated. It is shown that, in addition to the stable ordered quasicrystal and 1/1 cubic approximant, two more phases having orthorhombic symmetry coexist. The a and c parameters of both these phases are similar to the lattice parameters of the cubic approximant, whereas their b parameters are, respectively, three and four times larger than the c parameters. It is suggested that these phases evolve on account of local symmetry breaking of the cubic approximant phase, possibly due to ordering.     

Use of electron channelling contrast imaging to assess near-surface mechanical damage

The crystal structure of a cubic phase in the system Zn-Mg-Er has been solved by a combination of high-resolution electron microscopy and X-ray powder diffraction. This phase is considered to be related to that of the quasicrystalline phase. The structure consists of 448 atoms in the unit cell with lattice constant of a ₀ = 20.20Å and the space group is F43m. Important structural elements in the cubic structure are interpenetrating icosahedral units around Zn and Mg atoms and Frank-Kasper polyhedra around the Mg atoms. No giant icosahedral atomic cluster, such as the 136-atom Bergman cluster, was found in the stucture.     

Icosahedral quasicrystal in annealed ZnMgSc alloys

A new icosahedral quasicrystal has been found in Zn 85-x Mg x Sc 15 ( x = 3,4,5) alloys annealed at 922K for 5-100h. Electron diffraction and powder X-ray diffraction experiments indicate that this quasicrystal has a primitive icosahedral quasilattice (P type) and a six-dimensional lattice parameter a 6D =0.7115nm. The stoichiometric composition of the icosahedral quasicrystal was estimated to be close to Zn 80 Mg 5 Sc 15, since the icosahedral quasicrystal coexists in the x = 5 samples with small amounts of a MgZn 2 -type Laves phase and a Zn 17 Sc 3 -type cubic phase with lattice parameter a =1.3854nm. The latter is interpreted to be a 1/1-type approximant crystal of the icosahedral quasicrystal. The atomic cluster included in the Zn 17 Sc 3 -type cubic phase indicates a structural similarity between the Zn-Mg-Sc quasicrystal and the Cd-Yb (and Cd-Ca) icosahedral quasicrystals recently reported.     

Posttraumatic Stress,Posttraumatic Growth,and Satisfaction With Life in Military Veterans

Objective: Military veterans are more likely than civilians to experience trauma and posttraumatic stress disorder (PTSD). Research suggests, however, that some people who experience trauma, including veterans, report posttraumatic growth (PTG), or positive personal changes following adversity. In this study, we tested a comprehensive model of PTG, PTSD, and satisfaction with life in a veteran population, exploring the roles of challenges to core beliefs, types of rumination, sex, and time since event. Method: Data were collected via Amazon’s Mechanical Turk, an online crowdsourcing website, from veterans (N = 197) who had experienced a stressful event within the last 3 years (M = 16.66 months, SD = 12.27 months). Structural equation modeling was used to test an integrated conceptual model of PTG, PTSD, and satisfaction with life. Results: Results showed that challenge to core beliefs was directly associated with both deliberate and intrusive rumination. Deliberate rumination was positively related to PTG; intrusive rumination was positively related to symptoms of PTSD. PTG and PTSD, in turn, mediated the relationship between rumination styles and satisfaction with life; PTG was related to higher satisfaction with life; and PTSD was negatively related to satisfaction with life. Results failed to show differences on any model variables as a function of time since event or sex. Conclusion: Results indicate that the intentional facilitation of PTG may be a complementary and alternative option to the reduction of PTSD symptoms for improving satisfaction with life. Findings suggest that efforts to facilitate PTG should be focused on strategies for promoting deliberate rumination.     

New 1/1 cubic approximant phases in the Al-Cu-Ru-Si system studied by electron diffraction and high-resolution electron microscopy

Two types of new Al-Cu-Ru-Si 1/1 cubic approximant phases, both of which have cell parameters a=12.68A have been found in an as-cast Al_58.5Cu₁₈Ru_13.5Si₁₀ alloy. The two phases have sc and bcc structures respectively and are finely mixed in transmission electron microscopy observations. It is proposed that the sc structure is caused by ordering of atoms in the bcc structure.     

Formation of Ga–Pd–Sc icosahedral quasicrystal and approximant phases

ABSTRACT

We report the formation of an icosahedral quasicrystal and its approximant in the Ga–Pd–Sc alloy. The primitive-type quasicrystal with a six-dimensional lattice constant of 0.713?nm formed in the melt-quenched Ga₅₃Pd₃₀Sc₁₇ alloy, with a similar composition to that of the Ga₅₅Pd₃₀Sc₁₅ 1/1 approximant. The atomic-scale observation and chemical analysis of the 1/1 approximant by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy showed that the approximant consisted of Tsai-type clusters with a characteristic chemical ordering. Furthermore, a series of approximants were observed in the Ga₅₅Pd₃₀RE₁₅ alloys by replacing Sc with other rare-earth elements (REs) (RE?= Y, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu). These approximants, which have relatively small lattice constants and consequently smaller RE–RE distances compared with those for other RE-containing Tsai-type approximants, may be candidates for materials with novel electronic and magnetic properties similar to those observed in Au-based quasicrystals and approximants.     

When does priming justice promote forgiveness? On the importance of distributive and procedural justice for self and others

Two studies show that thinking about justice can both enhance and impede forgiveness, depending on whether thoughts about distributive and procedural justice for self and others are activated. In Study 1 (n = 197), participants expressed more forgiveness towards a prior transgressor when primed to think about justice for self or procedural justice for others, and less forgiveness when primed to think about distributive justice for others. Study 2 (n = 231) used an alternate priming method and replicated these effects by inducing an interpersonal transgression and measuring forgiveness intentions, emotions and behavior. Study 2 also showed that priming justice influences forgiveness especially when the perceived severity of an interpersonal offense is high. The current research shows that activating justice cognitions can enhance or impinge on forgiveness in predictable ways. We discuss contributions to emerging justice theory, potential implications, and future directions.